DC-to-DC converters are widely used in electronic devices. For example, many information technology devices include a DC-to-DC converter for converting bulk power from a battery, or from an off-line power supply, to a form suitable for powering a processor or other integrated circuit. Examples of DC-to-DC converters include, but are not limited to, buck-type DC-to-DC converters, boost-type DC-to-DC converters, and buck-boost type DC-to-DC converters.
Many DC-to-DC converters must support a wide range of load current magnitudes while meeting stringent voltage regulation requirements. For example, DC-to-DC converters used to power modern microprocessors often must maintain tight voltage regulation over a wide load current range. The load current may change dramatically in a short time period, such as due to the microprocessor transitioning between a sleep state and an active state.
DC-to-DC converters commonly operate in a continuous conduction mode (CCM), where current continuously flows through the converter's energy storage inductor. As known in the art, CCM operation promotes low ripple current magnitude and fast transient response. However, CCM operation often results in low efficiency at light load. Accordingly, some DC-to-DC converters operate in an alternative mode at light load, such as a discontinuous conduction mode (DCM), to promote light load efficiency. DCM operation is characterized by current flowing through the converter's energy storage inductor being zero during part of each switching cycle. As known in the art, DCM operation is typically more efficient than CCM operation at light load.
FIG. 1 illustrates one prior art buck-type DC-to-DC converter 100 including a DC-to-DC converter controller 102 capable of both CCM and DCM operation. DC-to-DC converter 100 further includes a switching circuit 104, an energy storage inductor 106, an input capacitor 108, and an output capacitor 110. DC-to-DC converter controller 102 includes a current deficit signal generator 112, which generates a current deficit signal 114. Current deficit signal 114 represents a difference between a current command signal of the DC-to-DC converter and an actual current signal of the DC-to-DC converter. An integration subsystem 116 integrates current deficit signal 114 to generate a modulator control voltage Vctrl at a modulator control node 118, which is electrically coupled to a modulator 120. Modulator 120 generates control signals 122, from at least modulator control voltage Vctrl and a clock signal. Control signals 122, which are, for example, pulse width modulation (PWM) signals or pulse frequency modulation (PFM) signals, control switching circuit 104 to cause DC-to-DC converter 100 transfer power from an input power source 124 to a load 126. Modulator 120 is capable of either CCM or DCM operation.